1. Field of the Invention
The present invention relates to programming content addressable memory utilizing phase change memory and separate word-line and search-line access elements.
2. Description of Background
Content addressable memory (CAM) is a type of computer memory utilized in high speed searching applications. Most CAM devices utilize transistors configured as static random access memory (SRAM), and additional transistor circuits for match operations. Typically in these CAM devices search line access transistors and word line access transistors are necessary to operate and program individual memory cells in the memory arrays. The search line access transistors and word line access transistors are often comprised of power intensive large drive field effect transistors (FET).
Phase change material can also be utilized to store information in CAM devices. Phase change materials can be manipulated into different phases or states, with each phase representing a different data value. Generally, each phase exhibits different electrical properties. The amorphous and crystalline phases are typically two phases used for binary data storage (1's and 0's) since they have detectable differences in electrical resistance. Specifically, the amorphous phase has a higher resistance than the crystalline phase.
One difficulty in using resistive memory elements, such as phase change memory, in CAM designs is the size of an individual memory cell and the number of lines (search-lines, word-lines, bit-lines, match-lines, and their complements) that must be utilized. Thus, it is beneficial to devise a CAM device that requires fewer lines. Additionally, it would be also beneficial to devise a CAM device that can also store ternary data.